1. Field of the Invention
The present invention generally relates to a sheet processing apparatus to bind together a bundle of sheets; an image forming system including the sheet processing apparatus and an image forming apparatus, such as a copier, a facsimile machine, a printer, or multifunction machine capable of at least two of these functions; and a sheet binding method used in a sheet processing apparatus.
2. Description of the Background Art
There are sheet processing apparatuses, so-called finishers or post-processing apparatuses, that align a bundle of sheets (hereinafter “a sheet bundle”) output from an image forming apparatus and bind the sheet bundle with metal staples. Such sheet processing apparatuses can automatically staple a number of sheet bundles on which images are formed and are widely used for convenience and efficiency thereof.
Additionally, there are hand-held staplers, so-called staple guns or powered staplers, capable of binding sheets without metal staples. A tooth form may be used to press multiple sheets so that fibers of the sheets tangle with each other and thereby tie the sheets together, or bind the sheets together using other types of processing such as half blanking, lancing, bending, and inserting. For example, JP-S36-13206-Y discloses a hand-held stapler capable of clamp binding, and JP-S37-7208-Y discloses a hand-held stapler that makes cut holes in sheets, bends cut portions, and inserts the cut portions into the cut holes.
Sheets bundles free of staples can be directly put through a shredder. Thus, such binding tools can reduce consumption of consumables, make recycling easier, and be effective to save resources. It is to be noted that, hereinafter clamp binding refer to a binding method that involves pressing multiple sheets with a tooth form to tie the sheets, thereby causing fibers of the sheets to tangle with each other. Use of clamp binding in sheet processing apparatuses is expected to increase owing to the above-described advantages.
In conventional approaches, a pressure lever that does not include a driving source is moved by a one-rotation cam to bind or bond sheets together.
For example, JP-2010-189101-A proposes a sheet binding device to bind a bundle of sheets by forming projections and recesses in the direction of the thickness of the sheet bundle, according to the thickness of the sheet bundle. Specifically, the sheet binding device includes a pair of tooth forms movable in the thickness direction of the sheet bundle, to squeeze the sheet bundle to form the projections and the recesses in the thickness direction, and a pressure applying member to apply pressure to the pair of tooth forms. The pressure is increased as the thickness of the sheet bundle increases.
Additionally, the pressure applied to the tooth forms may be increased as the thickness of the sheet bundle increases by a configuration that includes a rotary member, a driving source to rotate the rotary member, and a flexible member to apply pressure to the tooth form that is movable. The rotary member includes a contact portion that slidingly contacts the flexible member. As the rotary member rotates in one direction and the opposite direction, the amount by which the rotary member shifts to the flexible member increases and decreases, respectively. The rotational position of the rotary member can be changed to increase the shift amount of the flexible member as the thickness of the sheet bundle increases.
To bind the sheet bundle, the pressure lever is shifted in the former approach, and the pressure applying member including the rotary member applies pressure in the latter approach. In such configurations, typically the sheet bundle is pressed with a pressure of 1000 N or greater to cause the sheet fibers to tangle with each other. A motor may be used to generate the pressure.